I'm really looking forward to this season
I don't think Ash will be replaced, since he is shown in a new outfit, and i would be really sad after 13 seasons with Ash in front, and pokem0on would never be the same without Ash.
I think that Brock will be there too, and a new girl will join them. I'n not sure that it's the girl on the picture that will join them, since she looks quite different from the other girls.. maybe she's a person who only will appear in some episodes?
The new boy on the picture is maybe a new rival? I personally hope, that they'll make an interesting rival like Paul again. Maybe it's just a person like the new girl?
I think that Ash will take Pikachu with him, and maybe Gible. And he will get one of the new starters.
Maybe the new girl will pick the grass-starter this time, since the two previously girls have chosen Fire and Water, and Ash will get a Water-starter this time.
I can't wait till this season comes out